The output of a general power supply needs to rectify AC current to produce a stable DC current. To achieve the aforementioned objective, a basic structure should include at least one output switch unit, a transformer and a rear-end rectification unit to control the direction of AC current passing through a primary winding of a transformer to produce exciting cycles and demagnetizing cycles of the transformer. The secondary side winding of the transformer produces AC current with a voltage change, and finally the rectification unit converts the current into AC power, and supplies the voltage required for the operation of an electronic device. In an electric power conversion, the timing of the rectification unit is asynchronous with the timing of the output switch unit, and thus causing short circuits or unnecessary consumptions of power. A rectification unit in a conventional circuit is asynchronous, since it does not know the timing of the output switch unit. Referring to FIG. 1 for the basic structure of a conventional synchronous rectification converter, an output switch unit 3 at the front end of a transformer 4 includes a first output switch 31 and a second output switch 32, and the rectification unit 6 includes a first rectifier 61 and a second rectifier 62, and the working cycle of the first and second output switches 31, 32 is controlled by a pulse width control unit 1 to change the current passing through the transformer 4. The rear end of the transformer 4 detects a direction change of current at a secondary side of the transformer 4 by a plurality of detection circuits 5, so as to drive a plurality of rectification driving units 21 to change the operation conditions of the first and second rectifiers 61 respectively. The first output switch 31, the first rectifier 61, the second output switch 32 and the second rectifier 62 are turned ON or OFF simultaneously. However, the first output switch 31 which is turned ON in an operation has no way of knowing whether or not the second rectifier 62 is turned OFF before the first output switch 31 is turned ON. If the first output switch 31 is turned ON and the second rectifier 62 is turned OFF, then an excessively large current will pass through the first rectifier 61 and the second rectifier 62, until the second rectifier 62 is turned OFF. Now, the secondary side of the transformer 4 will produce a very large surge, which will damage the first and second rectifiers 61, 62, and thus it is necessary to enhance the timing and linking relation between the output switch unit and the rectification unit, so as to avoid abnormal currents produced in the electric power conversion, damages to components, or unnecessary consumptions of excessively large power.